The following abbreviations are used in the text below.
HSDPAhigh speed downlink packet accessHS-DSCHhigh speed downlink shared channelHS-PDSCHhigh speed physical downlink shared channelHS-SCCHhigh speed shared control channelQAMquadrature amplitude modulationQPSKquadrature phase shift keyingRNCradio network controllerSDMAspace division multiple accessUEuser equipment
The 3GPP Release-5/6/7 specifications define HSDPA with adaptive modulation where the used modulation is either QPSK or 16QAM depending on the Node B scheduler decision. See for example 3GPP TS 25.212 “Multiplexing and channel coding”. Recently the discussion on introducing also the possibility to use 64QAM with HSDPA has emerged in 3GPP. At the same time 3GPP is specifying a MIMO (multiple input-multiple output) multiantenna technique for HSDPA MIMO requiring some redesigning for the HSDPA related control channels.
The current HS-SCCH structure used to inform the format of the actual high speed downlink shared channel (HS-DSCH) transmission (including the used modulation) is split into two parts. Part 1 contains 8 bits, 7 bits to inform the used high speed physical downlink shared channel (HS-PDSCH) codes for the HS-DSCH transmission and one bit (QPSK/16QAM) informing the used modulation on those HS-PDSCH codes. Part 2 contains further information such as transport block size, hybrid automatic repeat request (HARQ) information, etc.
The high speed shared control channel (HS-SCCH) transmission starts 5120 chips earlier than the HS-DSCH transmission in order to allow the user equipment (UE) receiver to get the 1st part of the HS-SCCH before the HS-DSCH reception starts and thus know in advance the codes and modulation used on the HS-DSCH, as best shown in FIG. 1.
With HSDPA MIMO the intention is further to add at least two bits of the antenna weights used for the HS-DSCH transmission to Part 1 for giving also this MIMO specific information to the receiver. Also, one bit will be added to indicate the number of streams used i.e. single-stream or dual-stream transmission. The dual-stream transmission consists of a primary stream and a secondary stream. The modulation type (QPSK/16QAM/64QAM) for the secondary stream is always equal to or lower than the modulation of the primary stream. However, the first problem is how to add a new modulation (64QAM) indication to the part 1 of the HS-SCCH.
Moreover, multi-stream transmission enables the use of space division multiple access (SDMA) methods, where simultaneous data streams can be transmitted to different UEs. However, there is a second problem—how to inform different UEs that SDMA transmission is ongoing, because this knowledge is beneficial in the receiver design.
An example of a working assumption for defining the new HS-SCCH structure for MIMO operation may be seen at document R1-062485 entitled “Details of HS-SCCH signalling for Rel-7 MIMO”, from 3GPP TSG RAN WG1 Meeting #46 bis (Seoul, Korea, 9-13 Oct. 2006 by Philips).
One solution to the problem is to do as was done with the antenna weight bits with MIMO, i.e. make room for one additional bit to the part 1 by reducing the error correction coding of the part 1. See, for example, document R1-062935 entitled “Higher Order Modulation for HSPA—Impact on RAN1 specifications”, from that same 3GPP RAN1 meeting and by Ericsson.
Moreover, another prior art solution to the problem is to introduce one extra bit to signal SDMA operation. See, for example, document R1-062032 entitled “HS-SCCH in support of D-TxAA”, from that same 3GPP RAN1 meeting and by Qualcomm Europe.
There is a need in the art for a solution to these problems without substantially increasing the signalling overhead as in the above proposed solutions.